1. Field of the Invention
The invention relates to the vapor sterilization of articles such as medical devices with at least two open ends and a flow path therebetween, and more particularly, to a device and method for delivering a high flow of vapor sterilant into and through a lumen device with at least two openings and a flow path therebetween during the sterilization process.
2. Description of the Related Art
Medical instruments have traditionally been sterilized using either heat, such as is provided by steam, or a chemical, such as formaldehyde or ethylene oxide in the gas or vapor state. Each of these methods has drawbacks. Many medical devices, such as fiberoptic devices, endoscopes, power tools, etc. are sensitive to heat, moisture, or both. Formaldehyde and ethylene oxide are both toxic gases that pose a potential hazard to healthcare workers. Problems with ethylene oxide are particularly severe, because its use requires long aeration times to remove the gas from articles that have been sterilized. This makes the sterilization cycle time undesirably long.
Sterilization using liquid hydrogen peroxide solution has been found to require high concentration of sterilant, extended exposure time and/or elevated temperatures. However, sterilization using hydrogen peroxide vapor has been shown to have some advantages over other chemical sterilization processes.
In U.S. Pat. Nos. 4,169,123 and 4,169,124 sterilization methods are disclosed using hydrogen peroxide vapor at temperatures below 80.degree. C. Liquid hydrogen peroxide is vaporized and the hydrogen peroxide vapor is then introduced into the sterilization chamber by pressure differential.
The combination of hydrogen peroxide with a plasma provides certain additional advantages, as disclosed in U.S. Pat. No. 4,643,876, issued Feb. 17, 1987 to Jacobs et al. U.S. Pat. No. 4,756,882, issued Jul. 12, 1988 also to Jacobs et al. discloses the use of hydrogen peroxide vapor, generated from an aqueous solution of hydrogen peroxide, as a precursor of the reactive species generated by a plasma generator. The combination of hydrogen peroxide vapor diffusing into close proximity with the article to be sterilized and plasma acts to sterilize the articles, even within closed packages. Further, these methods of combining hydrogen peroxide vapor with a plasma, while useful in "open" systems, have been found to be inadequate to effect sterilization in articles having long narrow lumens, since the methods are dependent upon diffusion of the sterilant vapor into close proximity with the article before sterilization can be achieved. Thus, these methods have been found to require high concentration of sterilant, extended exposure time and/or elevated temperatures when used on long, narrow lumens. For example, lumens longer than 27 cm and/or having an internal diameter of less than 0.3 cm have been particularly difficult to sterilize.
The sterilization of articles containing long narrow lumens therefore presents a special challenge. Methods that use hydrogen peroxide vapor that has been generated from an aqueous solution of hydrogen peroxide have certain disadvantages, because:
1. Water has a higher vapor pressure than hydrogen peroxide and will vaporize faster than hydrogen peroxide from an aqueous solution. PA1 2. Water has a lower molecular weight than hydrogen peroxide and will diffuse faster than hydrogen peroxide in the vapor state. PA1 a sterilization chamber having an exhaust port; PA1 a source of liquid or vapor sterilant adapted to provide the sterilant in the sterilization chamber; PA1 a vacuum source with a vacuum valve to create a sterilization vapor from the sterilant, a negative pressure differential at the exhaust port of the sterilization chamber and an exhaust flow path out of the chamber; PA1 a gas and vapor flow conduit connecting one of the open ends of the device to a flow path of a vapor exhaust flow restrictor, such flow path allowing exhaust flow out of the sterilization chamber through the vacuum valve and vacuum source; and PA1 a vapor exhaust flow restrictor which allows part of the sterilization vapor to flow through the flow path of the device and thereafter out of the sterilization chamber through the vacuum valve and vacuum source and the remainder of the sterilization vapor to flow directly out of the sterilization chamber through the vacuum valve and vacuum source without passing through the flow path of the device. PA1 placing the device into a sterilization chamber having an exhaust port; PA1 connecting one of the open ends of the device to a first end of a gas and vapor flow conduit having a first and second end, the second end of which is connected to a flow path of a vapor exhaust flow restrictor, the flow path of the vapor exhaust flow restrictor allowing exhaust flow out of the sterilization chamber through a vacuum valve and vacuum source; PA1 introducing a liquid or vapor sterilant into the sterilization chamber; PA1 exposing the device to negative pressure with the use of the vacuum source for a time sufficient to provide sterilization vapor directly to the interior and exterior of the device, wherein the exposing can be before or after the introducing step; and PA1 exposing the device to negative pressure with the use of the vacuum source to create a negative pressure differential at the exhaust port of the sterilization chamber and the use of the vapor exhaust flow restrictor for a time sufficient so that part of the sterilization vapor flows through the flow path of the device and out of the sterilization chamber and the remainder of the sterilization vapor flows directly out of the sterilization chamber without passing through the flow path of the device whereby the device is sterilized.
Because of this, when an aqueous solution of hydrogen peroxide is vaporized in the area surrounding the items to be sterilized, the water reaches the items first and in higher concentration. The water vapor therefore becomes a barrier to the penetration of hydrogen peroxide vapor into areas such as long narrow lumens. One cannot solve the problem by removing water from the aqueous solution and using more concentrated hydrogen peroxide, since, among other reasons, concentrated solutions of hydrogen peroxide greater than 65% by weight can be hazardous due to the oxidizing nature thereof.
U.S. Pat. No. 4,952,370 to Cummings et al. discloses a sterilization process wherein aqueous hydrogen peroxide vapor is first condensed on the article to be sterilized, and then a source of vacuum is applied to the sterilization chamber to evaporate the water and hydrogen peroxide from the article. This method is suitable to sterilize surfaces, however, it is ineffective at rapidly sterilizing lumened devices, since it too depends on the diffusion of the hydrogen peroxide vapor into the lumen to effect sterilization.
U.S. Pat. No. 4,943,414, entitled "Method for Vapor Sterilization of Articles Having Lumens," and issued to Jacobs et al., discloses a process in which a vessel containing a small amount of a vaporizable liquid sterilant solution is attached to a lumen, and the sterilant vaporizes and flows directly into the lumen of the article as the pressure is reduced during the sterilization cycle. This system has the advantage that the water and hydrogen peroxide vapor are pulled through the lumen by the pressure differential that exists, increasing the sterilization rate for lumens, but it has the disadvantage that the vessel needs to be attached to each lumen to be sterilized.
In U.S. Pat. Nos. 5,492,672 and 5,556,607 to Childers et al, there is disclosed a process and apparatus respectively for sterilizing narrow lumens. This process and apparatus uses a multicomponent sterilant vapor and requires successive alternating periods of flow of sterilant vapor and discontinuance of such flow. A complex apparatus is used to accomplish the method. Additionally, the process and apparatus of U.S. Pat. Nos. 5,492,672 and 5,556,607 require maintaining the pressure in the sterilization chamber at a predetermined subatmospheric pressure.
In U.S. Pat. No. 5,527,508 to Childers et al., a method of enhancing the penetration of low vapor pressure chemical vapor sterilants into the apertures and openings of complex objects is disclosed. The method repeatedly introduces air or an inert gas into the closed sterilization chamber in an amount effective to raise the pressure to a subatmospheric pressure to drive the diffused sterilant vapor further into the article to achieve sterilization. The U.S. Pat. Nos. 5,527,508, 5,492,672 and 5,556,607 inventions are similar in that all three require repeated pulsations of sterilant vapor flow and maintenance of the sterilization chamber pressure at a predetermined subatmospheric pressure.
In U.S. Pat. No. 5,534,221 to Hillebrenner et al., a device and method for sterilizing and storing an endoscope or other lumened medical device is disclosed. The device includes a sealable cassette in which the endoscope or other medical device is placed. The cassette has an input port for receiving a sterilizing agent through a connector, an output port for expelling the sterilizing agent when a vacuum is applied thereto through a connector, and check valves in the input and output ports to open the ports when the connectors are coupled to the ports and to seal the ports when the connectors are removed from the ports such that after the endoscope has been sterilized, it remains sterilized within the cassette until the cassette is opened. The method of the U.S. Pat. No. 5,534,221 invention involves placing the medical device inside the cassette and coupling the device to either the input or output port of the cassette. The cassette is then placed in an outer oven-like container or warming chamber where the temperature is properly maintained. Connections are made to open the input and output ports on the cassette such that the sterilizing agent may be introduced through a first port to bathe the outside of the medical instrument or other object, such as an endoscope while one end of the hollow object, such as the endoscope, is coupled to the output port where a vacuum is supplied external to the cassette to pull the sterilization agent into the cassette and through the interior passageways of the endoscope. When the sterilization process is completed, the warming chamber is opened and the sterilizing cassette is simply removed from the chamber with the input and output ports being uncoupled from their respective sources. A tight seal is maintained and the object remains in the sterilized interior of the cassette until the cassette is opened or the device is to be used. The inlet and outlet ports also provide a means to supply and remove air and/or other fluids to and from the cassette during other non-sterilization phases of the process, such as warm-up and aeration. Plasma treatment steps are not included in U.S. Pat. Nos. 5,534,221 methods. Thus, the U.S. Pat. No. 5,534,221 invention is concerned with providing a means whereby a sterilized medical device can be retained within a cassette in which it was sterilized until ready for use, thus avoiding any contamination by exposure to the atmosphere or handling before use. Additionally, in some cases of the U.S. Pat. No. 5,534,221 invention, wherein the lumen of the device to be sterilized is connected to the output port, particularly wherein the devices have long, narrow lumens, the time to expel the sterilizing agent through the lumen and out of the cassette may be undesireably long. Also, in cases wherein the lumen device is very flexible, lumen collapse may occur, either slowing or preventing vapor exit or causing lumen damage.
Thus, no simple, safe, effective method of sterilizing smaller lumens exists in the prior art. In consideration of the foregoing, there remains a need for a simple and effective method of vapor sterilization of articles with both long, narrow lumens as well as shorter, wider lumens.